Message-ID: <3b9b90c6-f4ae-a7df-6519-847ea9d5fe1e@amazon.com>
Date: Fri, 2 Sep 2022 09:30:21 +0200
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Subject: Re: Add the ability to limit the amount of memory that can be
 allocated to backends.
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To: <reid.thompson@crunchydata.com>, pgsql-hackers
	<pgsql-hackers@lists.postgresql.org>
References: <bd57d9a4c219cc1392665fd5fba61dde8027b3da.camel@crunchydata.com>
From: "Drouvot, Bertrand" <bdrouvot@amazon.com>
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Hi,

On 8/31/22 6:50 PM, Reid Thompson wrote:
> Hi Hackers,
>
> Add the ability to limit the amount of memory that can be allocated to
> backends.

Thanks for the patch.

+ 1 on the idea.

> Specifies a limit to the amount of memory (MB) that may be allocated to
> backends in total (i.e. this is not a per user or per backend limit).
> If unset, or set to 0 it is disabled. It is intended as a resource to
> help avoid the OOM killer. A backend request that would push the total
> over the limit will be denied with an out of memory error causing that
> backends current query/transaction to fail.

I'm not sure we are choosing the right victims here (aka the ones that 
are doing the request that will push the total over the limit).

Imagine an extreme case where a single backend consumes say 99% of the 
limit, shouldn't it be the one to be "punished"? (and somehow forced to 
give the memory back).

The problem that i see with the current approach is that a "bad" backend 
could impact all the others and continue to do so.

what about punishing say the highest consumer , what do you think? (just 
speaking about the general idea here, not about the implementation)

Regards,

-- 

Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com